Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$24.84	10.243%	$27.3844	$27.38	$27.40	$27.40
Purchase #2	$160.47	11.439%	$178.8262	$178.83	$178.85	$178.80
Purchase #3	$102.51	4.421%	$107.042	$107.04	$107.05	$107.00
Purchase #4	$152.57	10.345%	$168.3534	$168.35	$168.35	$168.40
Purchase #5	$238.87	5.320%	$251.5779	$251.58	$251.60	$251.60
Purchase #6	$51.73	5.299%	$54.4712	$54.47	$54.45	$54.50
Purchase #7	$177.98	7.292%	$190.9583	$190.96	$190.95	$191.00
7 purchase totals =	$908.97		$978.6134	$978.61	$978.65	$978.70